The present invention relates to a cruise control apparatus for vehicles, and more particularly to a vehicle cruise control apparatus which is able to automatically carry out the shift operation of a transmission taking into account of the fuel consumption at each instant.
Vehicle cruise control apparatuses capable of controlling the speed of a car to maintain it at a desired or preset level are widely used. The cruise control apparatus according to the prior art is constituted in such a manner that the actual car speed is compared with the preset car speed and a car speed regulating member is controlled so as to reduce the difference between the actual car speed and the preset car speed to zero, the cruise control operation being carried out at the gear position selected by the driver.
Therefore, when a car which has been put under cruise control mode operation while traveling over level ground comes to an uphill climb, the engine has to assume a large load in order to output the desired driving power, so that fuel consumption is increased. Consequently, in such a case, the driver has to release the cruise control mode and then shift to the optimum gear position. Later he will have to restore the cruise control mode manually.
It is extremely inconvenient for the driver to have to shift to the optimum gear position manually when the car is operating in cruise control mode. Moreover, the manually selected gear position will not necessarily be the optimum position in terms of fuel consumption. Therefore, a high performance apparatus for cruise control which is free from this inconvenience and which assures optimum fuel economy has been desired.
An apparatus for automatically carrying out the gear change operation of a car is disclosed, for example, in Japanese Patent Application Disclosure No. Sho 58-81257. However, since the disclosed apparatus is intended to improve the feeling experienced by the driver when automatic gear change operation is carried out, the gear change operation is carried out without taking fuel economy into account so that the apparatus does not serve to reduce fuel consumption.